It is becoming increasingly apparent that entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae have considerable potential for the control of a variety of pest insects. Infective juveniles (J3) of these nematodes (which can survive for many months in the environment without feeding) are able to seek out insects, penetrate into an insect's haemocoel and there release specific symbiotic bacteria (Xenorhabdus species). The bacteria kill the insect within one to two days, and provide suitable conditions for nematode reproduction. R. A. Bedding has developed satisfactory methods for the large scale in-vitro mass rearing of these nematodes. His techniques have been described in, for example, the specifications of his U.S. Pat. Nos. 4,178,366 and 4,334,498, the specification of Australian patent No. 509,879, and his papers in Nematologica, volume 27, pages 109 to 114, 1981 (entitled "Low cost in vitro mass production of Neoaplectana and Heterorhabditis species (Nematoda) for field control of insect pests") and in Annals of Applied Biology, volume 104, pages 117 to 120, 1984 (entitled "Large scale production, storage and transport of the insect-parasitic nematodes Neoaplectana spp. and Heterorhabditis spp."). However, bulk, high density storing and transport of the nematodes has remained a problem.
In the Annals of Applied Biology paper noted above, Bedding described the use of crumbed polyether polyurethane foam as a carrier for stored nematodes in polyethelene bags. Unfortunately, nematodes stored in this way required constant forced aeration, extraction of the nematodes from the foam took one to two hours and the method was not suitable for the storage of Heterorhabditis species. T. Yukawa and J. M. Pitt, in the specification of International patent application No. PCT/AU85/00020, have described various methods of storing nematodes. Some of the information in that specification is based on previously published work and some results are not repeatable. However, one technique disclosed in that specification is certainly original, and works well for one species of nematode. That technique involves the storage of infective juvenile nematodes with powdered activated charcoal. The nematodes are then able to survive at high densities under anaerobic or substantially anaeroebic conditions for considerable periods of time. However, that method has a number of serious disadvantages, namely:
a) It works satisfactorily only with the species Steinernema feltiae.
b) Activated charcoal is extremely unpleasant to handle and packaging must take place in a fume cupboard. Recipients of nematodes packaged in this way also find the charcoal unpleasant to handle.
c) Activated charcoal is expensive.
d) The nematodes die within a few days if packages are exposed to temperatures higher than about 15.degree. C. (probably as a result of increased nematode activity depleting oxygen).
e) Problems arise if the packages contain more than about 60 million nematodes.
f) There are constraints on the thickness of packages, largely because nematodes survive well when mixed with charcoal only if there is a central mass of nematodes surrounded by an outer layer of charcoal, which does not occur in thick packages.